In recent years, progress is being made in research and development of diverse functional elements that use organic semiconductors. Organic EL elements are among the most common of such functional elements. An organic EL element is a current-driven light emitter that includes a pair of electrodes, consisting of an anode and a cathode, and a functional layer disposed between the pair of electrodes. The functional layer includes a light-emitting layer formed from organic material. Voltage is applied between the pair of electrodes. The emission of light from the organic EL element is caused by an electric-field light-emitting phenomenon taking place as a result of the recombination of holes injected from the anode to the functional layer and electrons injected from the cathode to the functional layer. Given the high visibility of organic EL elements resulting from their self-luminescence, as well as their excellent shock resistance resulting from the fully solid-state structure thereof, more attention is now being given to the application of organic EL elements as a light emitter for various organic EL display panels and organic EL display apparatuses or a light source.
In order to increase the light emission efficiency of an organic EL element, efficient injection of carriers (holes and electrons) from the electrodes to the functional layer is essential. Generally, provision of an injection layer in between each of the electrodes and the functional layer is effective in realizing efficient injection of carriers to the functional layer, since an injection layer has the function of lowering the energy barrier during injection. An organic material, such as copper phthalocyanine or PEDOT (conductive polymer), or a metal oxide, such as molybdenum oxide or tungsten oxide, is used as the hole injection layer provided between the functional layer and the anode. An organic material, such as a metal complex or oxadiazole, or a metal such as barium is used as the electron injection layer provided between the functional layer and the cathode.
Among such injection layers, an improvement in hole injection efficiency as well as longevity of the organic EL element has been reported for an organic EL element using a metal oxide, such as molybdenum oxide or tungsten oxide, as the hole injection layer (see Patent Literature 1 and Non-Patent Literature 1). A report has also been made regarding the influence on the improvement by the electron level formed by structures similar to an oxygen vacancy of the metal oxide on the surface of the hole injection layer (Non-Patent Literature 2).
On the other hand, as organic EL display panels grow in size, it becomes necessary to reduce the resistance of the wiring portion that connects the power source to the electrodes in the organic EL pixels constituting the panel. In particular, in a top emission type active-matrix organic EL display panel, it is necessary to use transparent electrode material, such as ITO or IZO, as the common electrode. As these materials are relatively high resistance, it is desirable to limit their use as a wiring portion.
With respect to this point, for example, Patent Literature 2 discloses a top emission type organic EL element with a wiring portion structured so that the second electrode (common electrode) is connected to auxiliary wiring, thus providing a wiring portion that reduces the use of the relatively high-resistance common electrode. The auxiliary wiring is low-resistance wiring that provides electrons from the power source to the common electrode.
It is desirable to provide the auxiliary wiring in a non-light-emitting area, so as not to block the light-emitting cell. Furthermore, the auxiliary wiring may be provided either above or below the common electrode in the non-light-emitting area. A structure in which the auxiliary wiring is provided below can be considered more desirable, as the auxiliary wiring can be formed during the same processes as when forming other components such as the thin-film transistors and pixel electrodes.